1. Field of Invention
This invention relates to the field of firearms, specifically accessories and mounting devices for firearms.
2. Prior Art
Several years ago the military started the SCAR program to select a weapon which would replace all rifles currently utilizing a direct impingement operating system in use by the military. In short, a replacement of the M16/M4 rifle was being sought.
To explain the difference in the two systems, both direct gas impingement rifles and piston driven rifles have a hole toward the front end of the barrel. As the cartridge is fired, burning propellant causes the bullet to move down the bore of the rifle. The propellant burns, generating expanding gases thereby increasing the pressure behind the bullet. As the bullet passes the hole in the barrel, some of the gas is tapped off. This is where the direct gas impingement and piston driven rifles become different.
In a direct impingement rifle the gas is directed by means of a long tube back into the receiver of the rifle. There is a cupped bolt carrier key which the tube fits into. The force of the gas pushes back the bolt carrier and reciprocates the rifle's self loading action. The disadvantage of this is dirty gases and carbon residues are deposited into the rifle's action and with sustained fire can lead to eventual failure as the close tolerance parts are caked with carbon. The long trip the gas must make before imparting its force also allows much of the gas to leak out of the system if parts are not mated exactly.
Rifles and carbines utilizing a gas piston system offer the user a more reliable, robust, controllable, cleaner operating system. As the gas is tapped off the barrel, it is immediately met by a gas piston. The gas drives the piston back which pushes a rod that actuates the action of the rifle. The gas piston uses all of the tapped gas to generate the rear momentum of the piston. Once it has moved back far enough with enough momentum to actuate the mechanism of the rifle, all excess gases are rapidly vented off. The rapid venting of all excess gases makes for an efficient and clean, self regulating system since about 5% of the volume of gas is actually used to operate the firearm. None of the hot, dirty gas or carbon enters the moving parts located in the receiver of the host firearm.
In recent years there has been industry-wide interest to incorporate a gas piston system into the M16/M4 type rifle and its variants. The push for this substantial change is due to the shortcomings which the direct gas impingement M16/M4 type rifle has shown in sandy environments and after prolonged use.
Traditionally the M16/M4 type rifle utilized a gas tube, well known in the prior art, which has a curve along its length thus allowing for the current generation of rail adaptor systems (RAS's) system and hand guards to function. Gas piston systems have to be relatively straight along the entire length of the piston utilized. This straight piston and related components necessitated the development of new methods for the attachment of a RAS.
The advantages of a gas piston system are readily apparent to those familiar with the prior art. Unfortunately the new system left the traditional M16/M4 rifle equipped with a gas piston system deficient in several areas in which it previously was proficient. Examples:                1. Lack of an ability to utilize existing free float rails, and tubes. If a traditional free float tube or rail were utilized it would prevent the users from accessing the gas operating system above the barrel for cleaning purposes. Free float tubes and rails are necessary to prevent pressure from bi-pods and other accessories from pushing the hand guard, tube or rail into contact with the barrel thus compromising the weapon's accuracy potential.        2. Also recognized is the inability of the user to mount accessories which would traditionally be attached to rail interface systems. A rail interface system traditionally consists of a closed tube secured at or near the receiver of the firearm with a variety of accessory mounting rails located about the periphery of the tube. Currently available rails do not interface with a gas system and/or do not allow for access to the operating system for maintenance.        3. Other rails currently available do not facilitate the user's access to the gas piston operating system for cleaning without the total removal of the free float device. Removal of the free floating rail in its entirety to clean the operating system of the weapon will result in a loss of zero, or the ability of the weapon to direct a discharged bullet to a desired location would be compromised. In effect a military user would be prohibited from cleaning his/her weapon while in a combat environment.        4. Many currently available rail adaptor systems are difficult to install requiring an armorer or gunsmith with special tools to do the work.        
Previous rail adaptor systems (RAS's) such as shown in U.S. Pat. No. 5,826,363 (Douglas Olson) have consisted of an aluminum tube which replaces the hand guards. The tube has a series of standard 1913 Picatinny slotted rails at the 3, 6, 9, and 12 o'clock positions along the longitudinal axis of the bore. These Picatinny slotted rails allow for the use and alignment of various accessories with the axis of the bore, an example being sighting equipment to increase the functional ability of the host firearm. The RAS allows the end user to customize the firearm for a mission or make employment of the rifle more ergonomic, effective and/or comfortable. A variety of RAS systems have been developed, predominantly for M16/M4 rifles and clones thereof. While not the first, U.S. Pat. No. 5,826,363 (Douglas Olson) is the first truly useful RAS system in that it is capable of mounting and carrying the modern load of combat accessories.
Examination of the prior art puts these systems into different categories. There are “conventional” designs that work with the standard hand guard retaining ring on the rifle (delta ring) and simply replace the hand guards. These systems are usually found to be two-piece designs, two semi-circular halves making up a tube. These designs transmit the weight of the accessories to the barrel of the rifle, changing the point of impact of the bullet. They also transmit external forces such as pressure from the user's hand, or force exerted by the weight of the rifle resting on a fixed support like a sandbag or bi-pod. Since these designs are mounted directly to the barrel and gas block, they transmit the heat from the barrel through the highly conductive aluminum alloy to the hand of the users.
The other general category of RAS's are one or two piece designs that use a proprietary system to clamp onto the rifle without contact with the barrel forward of the barrel nut allowing the barrel to “free float” and thus not affecting the point of impact by outside forces or the weight of the accessories mounted on it.
Once mounted, neither type of RAS is readily removable without some type of mechanical fixture and tool. None have provisions to allow easy access to parts underneath the top rail of the hand guard, leaving the user to abandon maintenance of the parts once the RAS is installed.
Mil. Std. 1913 covers specifications of the longitudinal rails affixed, molded, cast, extruded onto, or as part of the Rail Accessory System. The standard exists so that a host of manufacturers can design and manufacture accessories to easily affix to the rail and thus the rifle.
No prior art documents describe or illustrate a RAS which is readily adaptable to either a gas piston or direct gas impingement rifle design. None have made provision for a removable top rail to access the gas system for maintenance while free floating the barrel and providing clearance and ventilation for the gas system parts. There is no evidence of an RAS being conceived that could switch between rifles of one family to another with the use of simple conversion parts. No currently available RAS may be installed without a series of specialized tools.
3. Objects and Advantages
Accordingly several objects and advantages of the present invention are the proposed novel design for a new top opening, modular top rail, multi-rifle adaptable, free float Rail Adaptor System, or RAS as described herein. It was quickly recognized that the advantages of a gas piston system were negated by the fact that the user would not have the ability to use a RAS. A standard free float RAS cannot be used because gas piston systems require the user to remove, clean and maintain the parts of the gas system. All prior RAS designs were closed tubes or semi-permanent installations, not allowing clearance or access to the gas system.
The herein described RAS was conceptualized and designed to be a free float RAS which attaches to the receiver over the barrel nut and allows the user to open the top of the RAS and access the gas system parts for maintenance and service. Further, the herein described RAS allows for the use of Mil. Std. 1913 Picatinny rail mounted accessories such as back up sights, optical gun sites, lasers, vertical grips, etc. Outside forces such as the user's hand, a tensioned sling, or from resting the RAS on a stable surface such as a sand bag would not affect the firearm's point of impact. No other design is known which offers the above mentioned capabilities on a gas piston operated firearm.
(a) Modularity: The RAS system herein described has a removable top section that allows the rapid conversion of the RAS to different rifle designs which require clearance for their gas system. The user may choose a different top rail height for use with different sighting equipment or accessories. Further, different length rail sections may be added to meet the needs of the user and accommodate different barrel lengths. The RAS disclosed herein is designed to fit on a standard M4 carbine, M16 or other AR15 type rifle, well known in the prior art, and attached to the standard Mil. Spec. barrel nut which allows its use on a standard direct gas impingement system. This allows the purchaser of the herein described device an ability to acquire a single rail for use with either a direct gas impingement or a gas piston operating system. Further, the inventors of the rail have designed a variety of barrel nuts to allow the herein described novel invention to be adapted to other weapon systems.
Provisions are made to accommodate the remote switching requirements of some of the mounted accessories. Holes would be placed at various positions on the accessory adaptor rails that would allow pre-wiring of switching wires.
No other publicly known design offers this modularity between both gas piston operated rifles and direct gas impingement operated rifles.
(b) Ease of installation: To illustrate the claim of easier installation we will use the example of the M4 carbine. See FIG. 2 for an exploded diagram of the rifle mentioned. Free float RAS's already on the market require either the removal of the barrel, the front sight/gas block, the flash compensator/suppressor, delta ring, delta ring spring, delta ring retaining circle clip, hand guard retaining bracket or all of these to install the RAS. This varies with rifle model and make. None of these tasks can be performed without specific tools or a shop available to the end users. Knowledge and experience are required to complete installation of all free float RAS designs known, with the exception of the GG&G free float RAS and the TROY Industries RAS. Yet these RAS's do not readily allow access to the parts enclosed by the RAS, making them unsuitable for gas piston designs.
Examples of possible tools needed to accomplish installation of current RAS systems are as follows.                Vice        Barrel vice        A barrel nut wrench        Torque wrench        Cheater bar        Flash suppressor wrench        Drift punches        Hammer        Torch to heat and remove front sight/gas block        Headspace gauges        Barrel straightness gauge        Upper receiver vice fixture        
If not installed correctly by a competent armorer or gunsmith, the removal of the barrel assembly and other parts listed previously to install a conventional RAS can lead to disaster. Problems can include the gas tube being bent, barrel being bent, cross threading of the barrel nut during installation, or over-torque of the barrel nut.
The above claimed modular free float, top open RAS design only requires removal of the delta ring assembly and front hand guard bracket. This can be done with the most remedial tools as the delta ring and spring assembly could be simply cut off and disposed of as these parts are no longer necessary. The same holds true of the hand guard retaining bracket. The RAS is installed over the barrel nut with a top barrel nut clamp that is secured by 4 hex head machine screws with a standard inexpensive hexagonal wrench that can be supplied with the RAS for a nominal cost. Neither the barrel nor the gas system are disturbed and thus do not require any special tools, gauges or shop space. There is no risk to the integrity of the critical parts of the rifle system. Installation time is completed in minutes with minimal instruction, instead of hours by an experienced armorer or gunsmith. No other publicly known design offers ease of installation with the practical advantages this system offers.
(c) Ease and Cost Effective Manufacture: The herein described Modular Top Opening Free Float RAS has been designed to use cost effective aluminum alloy extrusion. All three major parts of this assembly are manufactured from the same extrusion profile. The extrusion profile can be cut to any desired length required by the end user with no change to the basic design. Having all parts by one extrusion profile ensures a tight fit and finish and cost effective manufacture that is very difficult to achieve by using separate manufacturing processes for each component. The extrusion profiles are cut and CNC machined to final specifications ensuring tight mating parts and parts compatibility. If stock extrusion profile material or extruding services are unavailable, the profiles may be manufactured from bullet aluminum by means of wire EDM cutting. No other publicly known or known patented system offers the ease or flexibility and cost effective manufacture with all mentioned practical advantages. Some of these processes are found in the prior art but there is no example found of a free float RAS where the clamping mechanism and complete tube are all made from a single extrusion. This speeds procurement to production and allows large or small orders to be filled on demand utilizing technology processes that are available by many machine shops in most US cities.
(d) Un-interrupted rail height, integrity and increased usable rail space yet retain the ability to easily remove or swing open the top half of the RAS: M4 carbines and some M16 rifles are equipped with an integral Mil. Std. 1913 rail longitudinally across the top of the upper receiver to allow mounting of a detachable carry handle, or optics and night vision equipment. This longitudinal rail across the top of the receiver is commonly referred to as a “flat top”. The herein described RAS has its top rail matched in height to that of the “flat top” found on the M4 and M16 rifles. This allows a continuous Mil. Std. 1913 rail from the rear of the receiver to the front of the RAS. This continuous rails allows the user to stack optics parallel with one another down the axis of the bore.
An example of this would be stacking a standard un-magnified night vision monocular mount on the Mil. Std. 1913 rail on the rifle upper receiver, with an unmagnified red dot optical sight on the RAS. Examples of this are found in the prior art. Examples such as the Lewis Machine and Tool “Monolithic Rail Platform” and the Troy Industries MRF-C do offer a continuous top Mil. Std. 1913 rail, but neither offers the ability to easily install and remove the 12 o'clock rail which allows access to the gas system parts or allows easy installation and removal of the RAS by the end users.
(e) Ventilation of gases and dissipation of heat: provisions have been made to provide adequate clearance for the gas piston systems on the rifles mentioned above. No RAS found or related prior art allows the proper clearance for the gas piston system to protect it, ventilate it, and allow for convection cooling of the barrel assembly and gas system. The H&K 416 rifle does have a rail which clears a proprietary gas piston system. The down side is that the height of the “flat top” and the top of the rail are increased thus changing the height of the rail to bore ratio. This will negatively affect calibrated optics such as the Trijicon ACOG, well known in the prior art, and very common in military, law enforcement and civilian circles.
Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.